Demi Lovato Was the Ultimate Superfan at Christina Aguliera's Concert: "Keep It Up Queen"

Demi Lovato could hardly contain her excitement on Friday as she enjoyed the opening night of Christina Aguilera's Las Vegas residency. Throughout the set, the 26-year-old "Confident" singer — accompanied by rapper Sirah and former Sonny With a Chance costar Matthew Scott Montgomery — shared videos of her singing along to some of Christina's greatest hits, including "Lady Marmalade" and "Fighter." She even shared a hilarious clip of her zooming in on her face as a single tear slowly fell down her cheek. One attendee also captured Demi energetically jamming out to "Ain't No Other Man" with her friends.

Later, Demi met up with Christina backstage and snapped a few selfies for the 'gram. "The f*cking queen herself. A PERFECT, perfect show.. couldn't believe it was opening night because it was so smooth, flawless and sounded incredible," she captioned a post. "Honored to call you a friend. Keep it up queen."

Demi and Christina definitely seem to have a special bond. In 2018, they dropped their feminist anthem "Fall in Line" — which Christina played during an intermission at her concert — and performed the duet at the Billboard Music Awards. Following the award show, Christina reflected on working with Demi on MTV's TRL, saying, "I needed somebody that not only could hit high notes, but also had meat to their tone. Demi had that, and I was like, 'Yes!' She killed the record." That's a pretty big compliment coming from the Xtina herself!